Furnace is used for smelting ores like Iron Ore and cook food like Raw Fish. A Furnace needs a fuel source like Oak Wood to smelt or cook. The player will need to have the furnace on the ground and then right click it to bring up the menu. The item they want smelted or cooked needs to be put on the top box while the fuel source is on the bottom box. A player is able to stack items in the furnace to be smelted.